Understanding Sea Surface Temperature Cooling in the Central‐East Pacific Sector of the Southern Ocean During 1982–2020
Xiaoqi Xu, Jiping Liu, Gang Huang
Abstract
Abstract Sea surface temperature (SST) in the Southern Ocean plays an important role in air‐sea interactions, forcing atmospheric variability. Using various observational and reanalysis data sets, we show that the SST cooling trend in the Southern Ocean (50°S–70°S) continues (∼0.3°C from 1982 to 2020). The largest SST cooling trend is in the central‐east Pacific sector, which can extend to 250 m. A detailed trend analysis for the mixed layer heat budget equation suggests that changes in the net surface shortwave radiation and Ekman horizontal advection are the two key contributors, though the other processes contribute to the SST cooling trend in winter and spring. The reduced downward solar radiation is largely due to the increase of cloud cover, which enhances shortwave‐cloud‐radiative feedback and decreases SST. Changes in Ekman advection associated with increased zonal winds is in favor of the colder water remaining in upper ocean layer.